1. Field of the Invention
The present invention relates to a navigation system.
2. Description of the Related Art
Conventionally, with a navigation unit that is mounted in a vehicle such as an automobile or the like, when the vehicle approaches an intersection or the like on the planned route, the navigation unit provides guidance by displaying arrows on a screen indicating going straight ahead, turning right, turning left, or the like, and/or by outputting the same information by voice. Also, a navigation unit has been proposed (e.g., Japanese Patent Application Publication No. JP-A-11-311535) that, when the vehicle enters an access road that will merge with the main thoroughfare of an expressway or the like, provides guidance regarding the merger with the main thoroughfare at which point the merging lane will end. A navigation unit has also been proposed that provides guidance for the access road segment (acceleration lane) that extends in advance of the point where the access road connects to the main thoroughfare and it becomes possible to change lanes into the main thoroughfare to the point where the acceleration lane ends, that is, information for the length of an acceleration lane. Because this allows the driver of the vehicle to know the length of the acceleration lane in advance, the driver can change lanes into the main thoroughfare safely and without worry.
However, in the conventional navigation unit, guidance information is provided only regarding the length of the acceleration lane, and not regarding the circumstances of other vehicles traveling on the main thoroughfare. Therefore, it is not possible for the driver who uses the navigation unit to judge whether or not the vehicle can safely change lanes, i.e. move from the acceleration lane to the main thoroughfare.